This research project is concerned with cardiovascular adaptations of chronically-instrumented dogs trained on aversive operant conditioning tasks which reinforce elevations in total peripheral resistance (ratio of mean arterial pressure to cardiac output). "Biofeedback" contingencies are programmed to each dog during daily sessions of up to 16 hours duration, which involve presentations of auditory stimuli paired with electric shocks whenever the total peripheral resistance decreases below a criterion level specified by the experimenter. Short-term (within sessions) and long-term (between sessions over periods of up to months) changes in systolic and diastolic pressure, heart rate, stroke volume, and cardiac output are investigated under these conditions. The experimental contingencies also provide the context for repeated measurements of water and food intake, hematocrit, osmolarity, and circulating levels of catecholamines, aldosterone, cortisol, sodium and potassium. Effects of these conditioning procedures upon respiration, EKG, skin temperature, and the sympathetic nervous system are also investigated. These relationships are studied to obtain information on basic behavioral-cardiovascular interactions, and to test the hypothesis that repeated exposures to environmental events which increase total peripheral resistance acutely will generate long-term changes in arterial blood pressure.